A time to digital converters (TDC) is a device that provides a digital representation of a time associated with events. For example, a TDC may be used to measure a time between a first event and a second event.
An implementation of a TDC may use a counter. The counter is started when the first event occurs and it is stopped when the second event occurs. The resulting count of the counter is a representation of the time between the first event and the second event. The time may be calculated by using the resulting count and the frequency of the clock received by the counter. In this type of TDC implementation, a higher clock frequency typically results in higher time resolution.
A TDC may be used, for example, in ranging systems that use time of flight (ToF) techniques to determine distance. For example, in ToF systems, a pulse of light is emitted and reflected off an object back to a photonic sensor, such as a single photon avalanche diode (SPAD). The time taken for the light to travel to the object and be reflected back onto the single photonic sensor may be used to determine the distance between the object and the device based on the known speed of light. A TDC may be used to generate a digital representation of the time between the transmitting of the pulse of light and the receiving of the light by the photonic sensor.